Communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or Mobile Stations (MS). Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression DownLink (DL) is used for the transmission path from the base station to the mobile station. The expression UpLink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
Dual Carrier Downlink (DCDL) was specified in 3GPP Global System for Mobile communications (GSM) Enhanced Data rate for GSM Evolution (EDGE) Radio Access Network (GERAN) Rel-7 as one part of the set of features called GERAN Evolution investigated in the feasibility study in 3GPP TR45.912, “Feasibility study for evolved GSM/EDGE Radio Access Network (GERAN)”. The feature introduces two parallel carriers transmitted on the DL to the same MS receiver.
The specification work on DCDL was mainly focusing on protocol aspects by simply extending the single carrier transmission to two separate carriers transmitted in parallel. Thus, any Radio Frequency (RF) related requirements were not modified. This, in effect also requires the terminal to implement two parallel receive chains, putting additional requirements on the analogue components in the terminal, increasing terminal cost.
However, a Multi-carrier DL proposal, such as that in GP-120691, “Downlink Multi-carrier for GERAN”, source Telefon AB LM Ericsson, ST-Ericsson SA. GERAN#55, makes use of a wider carrier selection filter, based on what is available from other wideband technologies, eliminating the need for separate components for the parallel carrier reception. With a wider carrier selection filter there is a need to relax current RF requirements to allow for cost efficient implementations.
Solutions on how to signal the multicarrier capability to the network and also how a set of rules can be specified to get a common understanding between the MS and the network on what carriers to receive at a certain point in time, are previously known. This is important for efficient usage of the spectrum in the case the maximum carrier separation is larger than the carrier selection filter.
Other solutions are based on a prioritized carrier.
These solutions discuss ways to utilize the limited MS receive BandWidth (BW) in a good way. The generalized problem itself can be quite challenging and one can imagine many simplified methods that would do an acceptable yet sub-optimal job with comparable results.
However, one of the more important considerations these days is to limit MS computational complexity. Thus, a solution that is good-enough from the perspective of performance, but that involves very low MS computational complexity would be particularly useful.
With a GSM DL multicarrier feature, a MS can receive data on several carrier frequencies simultaneously, see for example GP-120691, “Downlink Multi-carrier for GERAN”, source Telefon AB LM Ericsson, ST-Ericsson SA. GERAN#55. However, the feature is based on wideband receiver at the terminal side, and therefore, the MS would have a limited bandwidth where this is possible. Thus, a method is needed to select what carrier frequencies to receive given a GSM cell configuration. This problem has already been addressed but the known methods will not ensure a high number of carriers received, while at the same time achieving low computational complexity. A brute force method that searches through all possible carrier combinations, determining the optimum choice to achieve reception of the maximum number of carriers, can be quite demanding and might not be preferable in either network or MS implementations.
Frequency Hopping in GSM
The radio resource to use for a specific carrier assigned in GSM/EDGE is determined by the Mobile Allocation (MA), Mobile Allocation Index Offset (MAIO) and Hopping Sequence Number (HSN) for a hopping assignment, and the Absolute Frequency Radio Channel Number (ARFCN) for a non-hopping channel.
Below is a short description in words of the procedure in detail outlined in 3GPP TS 45.002, see 3GPP TS 45.002, for example, version 10.3.0, “Multiplexing and multiple access on the radio path”, section 6.2:
The MA contains a list of ARFCNs that the MS should hop over in its allocation, and the HSN contains the pseudo-random, pre-determined hopping sequence to use. The hopping sequence will be used by all connections assigned the same HSN. In order to ensure orthogonality between the assigned channels, each channel is assigned a unique offset to the assigned hopping sequence called MAIO (Mobile Allocation Index Offset). The ARFCN to use in a certain Time Division Multiple Access (TDMA) frame is determined by:mod(HSN(FN)+MAIO,N),
where N is the number of ARFCNs in the MA, and FN is the Frame Number.
The multicarrier proposal outlined in GP-120691, “Downlink Multi-carrier for GERAN”, source Telefon AB LM Ericsson, ST-Ericsson SA. GERAN#55 does not change the above described functionality but will extend the concept to apply to multiple carriers, i.e., a MS assigned in multi-carrier mode will, in each frame, potentially receive the same number of, different, ARFCNs as the number of carriers assigned. The most straightforward, and probable, implementation of the feature is to use the same HSN for all carriers but assign different MAIO values.
Further, compared to single carrier assignments, there will be a coupling between received bursts of a radio block, i.e., since the basic transmission format, a radio block, is transmitted over four bursts, often on different ARFCNs, the same carriers need to be received in all four bursts in order to be able to receive the full data block. That is, in order to avoid reception of fractional radio blocks. If a fractional radio block is received, the possibility to decode the payload carried by the radio block may be dependent on the channel coding used. This dependency may be avoided if only full radio blocks are received.